Influence of spray gun parameters on inflight particle's characteristics, the splat-type distribution, and microstructure of plasma-sprayed YSZ coatings

• Published in: Surface & coatings technology 2021-01, Vol.406, p.126705, Article 126705
• Main Authors: Tillmann, W., Khalil, O., Baumann, I.
• Format: Article
• Language: English
• Subjects: Atmospheric plasma spray (APS); Bonding strength; Ceramic coatings; Image analysis; Inter-splat contact; Lamellar structure; Melting degree; Microstructure; Morphology; Particle impingement characteristics; Porosity; Process parameters; Properties (attributes); Splat-type distribution; Splats; Spray guns; Substrates; Yttria-stabilized zirconia
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126705

Ceramic coatings, fabricated with specific properties using the atmospheric plasma spray (APS) process, are widely used for many applications in which the porosity and splat interfaces are the main factors affecting the performance. Since the coating microstructure is composed of large numbers of molten and semi-molten particles impinged successfully at the substrate (known as splats), the produced coatings are characterized by the melting degree of these particles and their relative splat-type fractions. In the present work, the effect of process parameters settings has been studied systematically, relating the characteristics of impinging particles to splat formation and eventually to microstructure development and properties of the coating. Therefore, individual splats were collected on mirror-polished substrates and observed using image analysis (IA). These were evaluated and categorized into different splat types, based on their melting degree and morphology, under each combination of spray conditions. It was found that gun current and standoff distance have a profound effect on the characteristics of impinging particles. These, in turn, determine the relative fractions of splat types, layered structure, and final properties of the deposit. The effect of splat-type distribution on the bonding strength between layers, lamellar structure, and coating porosity was investigated. •Splat is the main unit in plasma-sprayed ceramic coatings build up.•Splat morphology affects largely the inter-splat contact and layer bonding of the disposition.•Splat type distribution defines to a wide extent the quality and characteristics of ceramic coatings.•Relating spray parameters to inflight particles characteristics is necessary to relate them to the splat-type distribution.